[c-nsp] Growing BGP tables

[Bill Wichers]

> Maybe there are some Livingston engineers around who did BGP on the
> Portmaster3 that can give some ideas on memory usage.
>  From what I remember the PM3 was able to fit two full views (back
> then about 100k routes each) into 32MB of RAM.
>
> The minimum amount of space needed to store 140k routes is 1.6MB (4
> bytes for network, 4 bytes for netmask, 4 bytes for destination).
> The overhead per route must be huge.
>
> K

You are leaving out all the AS path / nexthop type info that BGP needs to
be able to do intelligent things with the route table. There's a lot more
in a multihomed router than just this->there type of stuff. I'm not sure
it would be possible to calculate a "minimum" memory needed for some given
number of routes, since you can't know exactly how much path info will
need to be stored with each route. You should be able to get *close* on a
large route table though by determining an average bytes/route which is
easily done from the info given in 'show bgp sum' on a Cisco box.

     -Bill



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Waveform Technology
UNIX Systems Administrator